1. Field of the Invention
The present invention relates to an electromagnetic pulse protection circuit capable of suppressing fast speed and low speed overvoltage spikes caused by electromagnetic pulses (EMP), and in particular to an electromagnetic pulse protection circuit having wave filtering capability.
2. The Prior Arts
In general, since the instantaneous rising speed of high voltage and large current signals are exceedingly fast, so that presently, the so-called lightning protection facilities are disposed in front of electronic communication devices, that belong to a kind of slow response lighting surge protection element (LS protection element), and usually are each composed of a spark-gap-switch or elements made of zinc-oxide. The major characteristic of LS protection element is that, in operation, its response time is rather slow, so that usually when its surge suppression function starts to work, the spike voltage has already been exceedingly high. As such, it does not provide timely and sufficient protection against fast rising voltage pulses.
Though, behind an ordinary IC circuit, a fast Electrostatic Discharge (ESD) protection device (ESD protection element, such as TVS, DIAC, or MOV, etc.) is provided for protection, and the response of this fast speed response protection element is rather fast, and it withstands a voltage of up to 8000V, however, it is not a very good current enduring element. In particular, the width of a pulse generated by lightning or man-made electromagnetic pulse bomb is rather wide, such that, long period of overvoltage will produce an excessive current effect in generating excessive heat. As such, the heat thus generated will first burn out an electrostatic discharge (ESD) protection device (fast response protection element), and then it will burn out the internal structure of semiconductor. Therefore, this kind of fast response protection element is only capable of withstanding electrostatic discharge, and it is not able to withstand various EMP attacks of high energies.
In general, communication equipments are provided with lightning protection device (namely, LS protection element), thus behind an IC circuit an electrostatic discharge (ESD) protection device (ESD protection element) is disposed for protection. However, even if an LS protection element and a fast response protection element are connected in parallel, yet this kind of arrangement is not effectively solve the problem mentioned above. Therefore, current will first flow to a fast response protection element of fast conduction, since current endurance capability of the fast response protection element is very much limited, thus it will be burned out quickly, thus the voltage will rise again. So the chances are, the IC circuit device disposed behind this arrangement has already been burned out before the LS protection element is activated to function. In addition, since a fast response protection element is a kind of capacitative element, the application of it will incur insertion loss to signals input to a communication equipment, hereby adversely affecting communication distance of the signals.
In order to solve the above-mentioned problem, the inventor of the present invention proposes a method of solution as disclosed in Patent Publication Number 588888 of Taiwan, ROC. Referring to FIG. 1, for a circuit diagram of a spike suppression circuit in an electromagnetic pulse protection circuit according to the prior art. Wherein, an electromagnetic pulse protection circuit is realized through connecting a fast response protection element 43 with an LS protection element 41 by means of a resistance element 42, and a compensation element 44 is series connected to the fast response protection element 43 from below. Since usually, fast response protection element 43 is of a capacitative type, therefore, it has the following disadvantages: while in middle frequency range, inferior fast spike discharge will occur due to the existence of inductance; yet in higher frequency range, bandstop effect will occur, and that is detrimental to frequency jumping applications for wide frequency band. For this reason, the inventor of the present invention subsequently discloses a new kind of electromagnetic pulse protection circuit, wherein, compensation is made further for an insertion loss caused by a fast response protection element 43, or otherwise, its structure is changed, as shown in FIG. 2. As such, this kind of arrangement is not only suppress an ordinary lightning strike, but it also prevents various kinds of fast EMP attacks, moreover, insertion loss is compensated; therefore, it is utilized in higher frequency range for withstanding and suppressing spikes of higher energies.
However, in order to achieve better protection against electromagnetic pulses, in the previous cases of prior art mentioned above, the impedance characteristics of impedance elements are utilized, yet the requirements of effectively suppressing electromagnetic pulses of various frequencies have not been fully met, thus it still has much room for improvements.